In recent, there has been known a technology that measures and visualizes velocity of fluid by using a particle image velocimetry (PIV) method. A PIV device visually represents flow of fluid, and is a technology that can measure, for example, instantaneous velocity of a tracer particle in a cross section of fluid. In this case, a tracer particle is dispersed in fluid, which is an object for velocity measurement, and a size of the tracer particle is small enough to sufficiently follow flow of the fluid. Meanwhile, the technology applied to the PIV device may be divided into a method that measures velocity based on an image photographed through a CCD camera and an echo PIV method that uses ultrasonic waves, according to an optical method.
For example, the echo PIV device radiates an ultrasonic beam to target fluid, and determines gradation of an ultrasonic image based on intensity of an echo signal radiated by an ultrasonic contrast agent dispersed in the target fluid. In addition, a position of a scatterer in the traveling direction of the ultrasonic beam can be identified from a period of time from radiation of an ultrasonic signal to reception of an echo signal.
However, there may be the case where it is difficult to exactly measure velocity of fluid depending on an environment where the PIV method is used, e.g., characteristics of the fluid.
For example, there may be difficulty in measuring blood flow velocity within the left ventricle by using the echo PIV device. That is, if any tissue of the left ventricle radiates an echo signal having similar intensity to that of the tracer particle, it is difficult to clearly discriminate an acquired ultrasonic image, and there may be the possibility that an error will occur in measuring the velocity.
In this regard, Korean Patent No. 1136814 (Title of Invention: A Method for Estimating a Hemorheological Factor of Blood Flow by Using a Red Blood Cell as a Tracer Particle) describes: a first stage of photographing and storing two (2) blood flow images for a red blood cell flowing within a blood vessel at a certain time interval by using particle image velocimetry (PIV); a second stage of calculating an instantaneous velocity field from displacement of the position of the red blood cell observed in each of the images photographed in the first stage and the time interval for photographing the two (2) images; a third stage of determining a velocity field distribution function, which is a radial coordinate function of the blood vessel, after curve fitting from an average velocity field, which is an average of a multiple number of the instantaneous velocity fields calculated in the second stage; a fourth stage of determining a shear rate from the velocity field distribution function; and a stage of determining a hemorheological characteristic from the shear rate determined in the fourth stage so as to predict a disease.